Pace the length of the wall desired on a section of yard or garden. Choose an area with proper drainage and without impediments such as tree roots. Lay a block of your choice at the beginning and end of the wall length. Cinder blocks -- also called concrete blocks or "CMU" (concrete masonry unit) -- come in a variety of sizes and variations. The standard size is 8-by-8-by-16 inches, but larger sizes work equally well.
Measure 1 inch on both the front and back sides of the blocks previously placed. Drive stakes on the outside edge of the 1-inch marks. This indicates the width of the trench needed for your sitting wall.
Dig between the stakes, both width- and length-wise, until your trench is 6 to 8 inches deep. At this point you should have passed the dark topsoil and be well into the lighter-colored subsoil.
String a line level on a length of twine. Tie the twine between the first and last stakes when the line shows level. Use this string to measure down to the bottom of the trench every 6 to 8 inches. If the bottom of the trench is level, the measurements will remain the same. Alternatively, lay a 2-by-4-inch board or other straight edge in the trench and place a carpenter's level on top. Adjust it by digging a little more out or replacing a bit of dirt as needed until the trench bottom is level.
Spread a layer of substrate, approximately 3 to 4 inches deep, inside the trench. Use deteriorated limestone with stabilizer or, better yet, deteriorated limestone with resin, which sets in a hard pack that doesn't readily shift. You may use paver base -- simply crushed and powdered stone -- instead; however, minus a concrete footing, rock mixed with resin works best.
Tamp the rock down level with your foot or a board and hammer. Follow by hosing down the rock with water to activate the cement-like properties. Allow the rock to sit for about an hour before proceeding.
Set the first block in place, positioning it with the open chambers facing upward. If using a solid block, lay the blocks on the widest face. Spread grout along the edge that will touch the next block and place the next block in line.
Measure down from the line level to the first two blocks to check if it's level. Alternatively, lay a 2-by-4 across the blocks to check. Tap either the board or the block with a hammer to set the block into the substrate. Use a rubber mallet if striking the blocks directly.
Continue the length of the wall, spreading grout across each edge and checking the level before tapping the block in place. When finished, each block should be about half below ground surface.
Fill the open holes with either more concrete grout or rock with resin. Use a long screwdriver or other rod to plunge up and down as the material fills the holes, working air pockets out. Let the wall set an hour or more to harden slightly.
Shovel dirt back around the base of the wall, filling in the extra inch clearance around the blocks. Tamp the dirt down with your foot as you work, taking care to not shove against the blocks and move them.
Cut a block to begin the next course. Position a chisel or a flat-head screwdriver halfway across the block. Strike softly with a hammer, re-positioning repeatedly to create a score line across the block face. Strike one final blow to encourage the block to crack apart appropriately. Blunt the broken edges with a hammer until flat. Alternatively, purchase half blocks already cut to size.
Spread grout along the bottom and the edge that will join the next block. Set the block in place. Continue across the wall length repeating the process. Begin with a partial brick to force the block joints to stagger and create greater strength.
Fill the block cavities, if applicable, with additional grout or substrate. Tamp down and work the material to force air pockets out.
Repeat each layer until the wall is just short of the height you want it -- typically 18 to 24 inches above ground level for a normal sitting wall. Using 8-by-8-by-16 blocks, you might choose three courses of blocks topped with a capstone. Allow in the final wall height measurements for the thickness of the final layer and for the portion of the first block buried underground.
Spread grout across the top layer of blocks before laying a coping, or the portion that you sit on. Place thin solid blocks, normal blocks laid perpendicular to the wall, flagstones or any stone or masonry product you choose in the grout. Allow the wall to sit and the grout to harden at least 48 hours before using.